Human Biology Sylvia S Mader Michael Windelspecht Chapter
Human Biology Sylvia S. Mader Michael Windelspecht Chapter 14 Senses Lecture Outline Part 2 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. 1
14. 4 Sense of Vision 1. Layers of the eye: Sclera • _______ – the white of the eye that maintains eye shape – Cornea: transparent portion of the sclera that is important in refracting light – Pupil: a hole that allows light into the eyeball 2
14. 4 Sense of Vision 2. Layers of the eye: Choroid • Choroid – middle layer that absorbs light rays not absorbed by the retina – ____: donut-shaped, colored structure that regulates the size of the pupil – _______ body: structure behind the iris that contains a muscle that controls the shape of the lens • Lens – attached to the ciliary body; refracts and focuses light rays 3
14. 4 Sense of Vision The lens • The lens is a flexible, transparent, and concave structure. • Visual accommodation occurs when the lens changes shape to focus light on the retina and form an image. • As we age, the lens loses elasticity, and we use glasses to correct for this. 4
14. 4 Sense of Vision The lens Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. ciliary muscle relaxed lens flattened light rays suspensory ligament taut a. Focusing on distant object ciliary body ciliary muscle contracted lens rounded b. Focusing on near object Figure 14. 7 Focusing light on the retina of the eye. suspensory ligament relaxed 5
14. 4 Sense of Vision 3. Layers of the eye: Retina • The retina contains photoreceptors called rods and cones. • _____ are sensitive to light. • ______ require bright light and respond to wavelengths of light (color). • The _______ is an area of the retina densely packed with cones where images are focused. 6
14. 4 Sense of Vision 3. Layers of the eye: Retina • Sensory receptors from the retina form the optic nerve that takes impulses to the brain. • The ______ is where the optic nerve attaches; it lacks photoreceptors. 7
14. 4 Sense of Vision Anatomy of the retina Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. sclera choroid rod cell and cone cell layer bipolar cell layer retina optic nerve ganglion cell layer blind spot a. Location of retina b. Micrograph of retina axons of ganglion cells to optic nerve © Biophoto Associates/Photo Researchers, Inc. light rays Figure 14. 9 The structure of the retina. 8
14. 4 Sense of Vision Photoreceptors of the retina • Rods – They contain a visual pigment called rhodopsin. – Rods are important for peripheral and night vision. – Vitamin A is important for proper functioning. • Cones – They are located mostly in the fovea. – Cones allow us to detect fine detail and color. – 3 different kinds of cones containing red, green, and blue pigments. 9
14. 4 Sense of Vision Rods and cones in the retina Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. ion channels close membrane of disk cas light rays rod cell outer segment cone cell cad e ctions of rea ion channels in plasma membrane retinal inner segment cell body opsin nucleus a. 20 μm synaptic vesicles synaptic endings membrane of disk rhodopsin molecule (opsin + retinal) b. © Lennart Nilsson, from The Incredible Machine/Scanpix Figure 14. 8 The two types of photoreceptors in the eye. 10
14. 4 Sense of Vision Summary of eye structures 11
14. 4 Sense of Vision Abnormalities of the eye • ________ – genetic abnormality in which colors, usually red and green, cannot be distinguished; most common in males • _____ – lens of the eye is cloudy • _____ – fluid pressure builds up in the eye 12
14. 4 Sense of Vision Abnormalities of the eye • Astigmatism – condition in which the cornea or lens is uneven, leading to a fuzzy image • ____sightedness – eyeball is too long, making it hard to see far away objects • ____sightedness – eyeball is too short, making it hard to see near objects 13
14. 4 Sense of Vision Abnormalities of the eye that are corrected with lenses Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. normal eye Long eye; rays focus in front of retina when viewing distant objects. Concave lens allows subject to see distant objects. a. Nearsightedness normal eyeball Short eye; rays focus behind retina when viewing close objects. Convex allows subject to see close objects. b. Farsightedness Figure 14. 11 How corrective lenses correct vision problems. Uneven cornea; rays do not focus evenly. c. Astigmatism Uneven lens allows subject to see objects clearly. 14
14. 5 Sense of Hearing Anatomy of the ear • The ear functions in hearing and balance. • 3 divisions 1. Outer ear: functions in hearing; filled with air 2. Middle ear: functions in hearing; filled with air 3. Inner ear: functions in hearing and balance; filled with fluid 15
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